THE EFFECTS OF ADSORBED WATER ON DYNAMIC-MECHANICAL PROPERTIES OF WOOD

The storage modulus and the loss tangent of Sitka spruce wood (Picea S itchensis) in the longitudinal direction at various moisture contents were measured at 20 degrees C, and the effect of adsorbed water was in vestigated by using a uniaxial rheological model to eliminate the cont ribution of matrix swelling. The largest Value for Young's modulus of matrix was obtained at around 8% moisture content. The rearrangement o f matrix molecules accompanied by the adsorption of hydrated water inc reased the value of Young's modulus up to about 8% moisture content, w hereas the plasticization of matrix molecules by the adsorption of dis solved water decreased it at above 8% moisture content. The loss tange nt of matrix had two peaks at similar to 1% and 20% moisture contents. It was considered that the former was due to the motion of the adsorb ed water itself and the latter to the relaxation related to the micro- Brownian motion of matrix substances, especially hemicelluloses. (C) 1 998 Elsevier Science Ltd. All rights reserved.